EDIT: The post below is a bit redundant now, I'm building a 3' Cub from the plan in Kelvin Shacklock's book "Aircraft Workshop: How to build models that fly." The book is quite simply excellent.

Yep, I'm finally biting the bullet. Whether it flies or not I'm going to build a plane from scratch. I don't fully understand 90% of the principles, but in my experience there's no better way to learn than to just dive in. I've read around alot, especially the articles at Airfield Models.

So, the mission, should I choose to accept it: build an EP trainer using the gear from my now retired GWS Pico Toger moth. I'm feeling ready to advance to a secondary tariner, but my girlfriend had a flying lesson yesterday and loved every minute so it would be good to build her a trainer to learn on. The death of the moth was not her fault I must add (she was darned good after 20 mins, touch and go circuits? Yes please. Stall recovery? Didn't even break a sweat.), I shorted the battery somehow while packing up and the burn made me drop the model which kamikazed on the ground. I never liked it much anyway, so I thought "stuff it I'll build a better plane."

Next, the specification - or at leat as much of a spec as I can understand.

I really hope that makes sense to the experienced builders here. I can more or less picture how I want the model to fly and I hope those numbers are on the mark. Please feel free to suggest modifications to them. If no one can find any serious flaws in that spec then I can start the drawings . I'm looking forward to seeing your responses and to getting started.

Thanks for the point about construction, I've added it to the spec. It'll be built up balsa with tissue or film covering . I think I've over estimated the weight, to be honest it's difficult to give an estimate with such little experience. I basically took the weight of the hardware and doubled it. It may well be that I can build it lots lighter than that. I should weigh the moth and set that as my target perhaps.

Since you already own the motor, ESC, and battery, I think you should just build the model and see what you end up for weight. I do think that 16% chord thickness will give you too much drag at your slow speeds and would recommend ~12%.

I'm not a particularly light builder so I'll limit my comment about total weight to my belief that 9oz is optimistic for a wing of that size, a fuselage that has volume and a landing gear. I would guess that a total fly-away weight of 12oz (for a balsa structure with covering) is more realistic. That weight would put the wing loading around 7.4 oz/sq ft - a bit more realistic number for a powered trainer since performance gliders have wing loadings around 5 oz/sq ft.

Alan

Please consider my comments as a challenge to see how light you can build the plane rather than possible discouraging comments. I think it is more important for you to build according to your beliefs and learn from that rather than modifying your beliefs too early.

Thanks for the comments , don't worry I'm totally new to the numbers game so I know they may be very different in the end.

In fact I have had something of a change of heart. I bought Kelvin Shacklock's book, and having marvelled at the models within I've decided to try to follow it. Sure, many things will be slightly out of date and I'll work around those but the fundamentals seem very sound. The first "real" project (I'm going to skip the chuck glider bit I think I could handle that!) is a 3ft span balsa Piper Cub. My girlfriend saw the Cub logo and insisted I build it (not that I needed much persuasion.)

So, I will be following Kelvin's plan, but i'm sure I will need help and feedback along the way. Not least because this plan is for rubber power and the conversion to EP may have many pitfalls. I went to my local and bought all the materials I need, except tissue which I forgot. I've sanded of my work bench and laid a nice piece of MDF over it which I will cover with cork tiles. Once that's all done I'll be ready to rock !!

Ok, yesterday was productive. My workshop is (nearly) pristine, the workbench and cork board is set up and the plans are all printed. Tonight I'll stitch the plan tiles together and transfer the cutting templates to the balsa. This is getting exciting!

Will,
I looked up the Cub in Kalvin's book last night. It reminds me of the first plane I built (rubber band powered) and the one that got me hooked in this hobby. The outline of individual parts in the parts layout sheets make the build almost like a kit.

Did you use a copy shop to enlarge the plans? I ask because if you did (and the print is made of graphite from a 'Xerox' machine) you might want to try transferring the parts layout sheet directly to the balsa sheet using a hot clothes iron (as he shows in another part of the book). I did not have much luck with the technique and ended up tack-gluing the layout sheet to the balsa and cutting through the sheet.

When you build the wing, I suggest you add turbulator strips (those 1/16th sq strips running the length of the wing in front) as in http://www.rcgroups.com/forums/attac...mentid=2412741 I found the film covering sagged quite a bit between ribs in this area. You can cut slots in the ribs with two hacksaw blades held together when the ribs a stacked with the main 'spar' for sanding as shown in his book.

I scanned the pages and then enlarged them in photoshop and matched them precisely to a ruler so they are bang on 200%. I printed the cutting templates on my ALPS printer, which uses a wax based ink which means it should transfer perfectly to the wood under heat (or at least that's my theory.) I was thinking of adding that extra strip, for a little extra rigidity and to help the tissue as you suggested. Thanks for the link .

The book is very well laid out, it's not perfect but anyone with a brain can fill in the blanks. I like all the models in there and I would be very proud indeed to build and fly all of them. I especially like the Spirit of St. Louis and the Sea Fury.

Ok today's job is to attatch battens to the underside of my build board, my workbench isn't flat enough. I'll get a propper metal one when I have a propper workshop, when my ship comes in etc and so on. Then I'll start cutting.

A question just occured to me, can you thin down dope with cellulose thinners and spray it onto tissue with a spray gun? That would give a nice even coat and it would be great if I could.

Well, mission one was sucessful. However the parts transfer thing didnt work at all. Kelvin neglected to mention in the book that the ironing techniqe doesn't work with an inkjet printer . I'll have to go to the printers in town on monday and get them to do it on their big laser printer. I was tired of stitching tiles together anyway.

And yes, you can spray dope with an airbrush if you thin it out: something like 1 part dope to 2 (or 3) parts thinner. Before airbrushing, you will need to brush thinned dope (1 part dope: 2 parts thinner) over the tissue until the pores are sealed. And before covering, you will need to apply dope to the edges of the piece you want to cover before doping the tissue on the piece.

I'll have to go to the printers in town on Monday and get them to do it on their big laser printer. I was tired of stitching tiles together anyway.

I hope you don't have any problems with copyrights. I did not notice any copyright waiver statements on the parts sheets.
If they won't copy it, let me suggest that you use use tacky spray on the backside of the parts sheets, stick the sheets to the balsa and cut through the pattern lines. In addition, the heat/dry transfer method did not leave enough graphite on the balsa to be very visible.

Copyright shouldn't be a problem as I'm not selling the plans. The author expects you to photocopy and enlarge the plans anyway, so I don't see that harm in getting a pro to do it . They came out very nicely, and I can get started now.